9V batteries can be (but sure will NOT) connected to each other.
(safety : you expose yourself in burns doing it)
Step 1: Soldering
The plastic plate was a little bit to wide, so I cut it to make it fit.
Solder two wires, each to the appropriate connector.
The battery used some paper to insulation the metal parts.
I keep some for the same reason.
Step 2: Housing
I cut two holes, as tight for the connectors as possible, because they will expend
in the shrink process.